%%
%% The LaTeX Companion, 3ed
%%
%% Example 6-7-15 on page I-485 in "siunitx --- Scientific numbers in tables".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{183.0pt}
\setlength\parindent{0pt}
%StartShownPreambleCommands
  \usepackage{siunitx}
%StopShownPreambleCommands

\begin{document}
  \begin{tabular}{|S|S[table-format=1.4]|
   S[table-format=1.4,table-number-alignment=left]|
   S[table-format=1.2,table-number-alignment=right]|}
  {default}&{Heading} &{Heading}&{Heading} \\
    2.3456 &  2.3456 &  2.3456 &  2.3456   \\
    4.2    &  4.2    &  4.2    &  4.23     \\
    6.783  &  6.783  &  6.783  &  6.783    \\
   -1.47   & -1.47   & -1.47   & -1.47
  \end{tabular}
\end{document}
